Fragrance has been described as having three sets of notes that make a harmonious scent accord. The notes unfold over time, with the first impression of the top note followed by deeper middle notes, and base notes appearing last. The olfactory and psychological sensation of a user depends, in part, on the user's mood when she or he is wearing the fragrance.
Scents that are perceived immediately upon application of a perfume are top notes. Top notes typically include molecules that evaporate quickly. Top notes form a user's initial impression of a fragrance. Heart notes form the main body, i.e. middle notes, of the fragrance. Base notes are typically not perceived until about thirty minutes from application of the fragrance. Base notes tend to be more complex than top notes or middle notes. Changes made in each of the notes impart change in scent to the other notes as well.